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912ULS friction torque

 
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JonathanMilbank



Joined: 14 Apr 2012
Posts: 383
Location: Aberdeen area

PostPosted: Sat May 05, 2018 12:50 pm    Post subject: 912ULS friction torque Reply with quote

Using a calibrated fish weighing scale at 30" and after locking the crankshaft, while pulling steadily at right angles I once again got a reading of a couple of pounds over maximum; about 15 lbs instead of the recommended 13.2.

I have an Airmaster hub with Warp Drive blades and the engine and gearbox have done over 200 hours since installation. The whole combination runs smoothly, with only a slight buzz somewhere above 3000 rpm and which smooths out again above 4000.

I've just done another oil and filter change which, as before, showed only a few pin-prick sized metal particles in the filter after being cut open. Same as always, with the particles being attracted to a strong magnet. There was only a little dark "dust" on the magnetic plug, similar to before.

Cylinder compressions were from 195 to 205 psi. Considering that all seems well and satisfactory, even though the anticipated reduction in friction torque with usage hasn't happened, should I be happy and just let sleeping dogs lie? What's wrong with having the torque so high?


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Burrilla



Joined: 25 Apr 2015
Posts: 181

PostPosted: Sat May 05, 2018 9:59 pm    Post subject: 912ULS friction torque Reply with quote

From the ROTAX Maint Manual:
"Calculate friction torque (Nm) by multiplying the force (N) obtained on the spring scale by the distance the scale is attached from the center of the propeller (L).
The friction torque must be between 30 Nm and max. 60 Nm (22 to 44.3 ft.lb). See calculation example." Where have you got the 13.2 from?

Regards

Alan Burrill




Quote:
On 5 May 2018, at 21:50, jonathanmilbank <jdmilbank(at)yahoo.co.uk (jdmilbank(at)yahoo.co.uk)> wrote:
--> Europa-List message posted by: "jonathanmilbank" <jdmilbank(at)yahoo.co.uk (jdmilbank(at)yahoo.co.uk)>Using a calibrated fish weighing scale at 30" and after locking the crankshaft, while pulling steadily at right angles I once again got a reading of a couple of pounds over maximum; about 15 lbs instead of the recommended 13.2.I have an Airmaster hub with Warp Drive blades and the engine and gearbox have done over 200 hours since installation. The whole combination runs smoothly, with only a slight buzz while passing above 3000 rpm and which smooths out again above 4000.I've just done another oil and filter change which, as before, showed only a few pin-prick sized metal particles in the filter after being cut open. Same as always, with the particles being attracted to a strong magnet.Considering that all seems well and satisfactory, even though the anticipated reduction in friction torque with usage hasn't happened, should I be happy and just let sleeping dogs lie? What's wrong with having the torque so high?Read this topic online here:http://forums.matronics.com/viewtopic.php?p=479873#479873



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JonathanMilbank



Joined: 14 Apr 2012
Posts: 383
Location: Aberdeen area

PostPosted: Sun May 06, 2018 3:27 am    Post subject: Re: 912ULS friction torque Reply with quote

Well spotted, thanks Alan. I didn't have the manual with me and looked up the info on a friend's tablet. In so doing I clearly selected info from an out of date source. So in fact my propeller friction torque is within limits. I think the clue to my error is in the word "legacy" below.

https://legacy.rotaxowner.com/si_tb_info/serviceinfo/3kul97.pdf


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